Sci­en­tists are in­ves­ti­gat­ing KOI-500, a plan­e­tary sys­tem they say crams five plan­ets in­to a re­gion less than one twelfth the size of the Earth’s or­bit.

Darin Ra­goz­zine, a post­doc­tor­al re­search­er at the Uni­vers­ity of Flor­i­da, pre­sented find­ings about the sys­tem Oct. 15 at the an­nu­al meet­ing of the Amer­i­can As­tro­nom­i­cal So­ci­ety’s Di­vi­sion for Plan­e­tary Sci­ences in Re­no, Nev.

The five worlds or­bit their host star so closely that their years, the time they take to cir­cle it, are meas­ured at only 1.0, 3.1, 4.6, 7.1, and 9.5 days. All five “zip around their star with­in a re­gion 150 times smaller in ar­ea than the Earth’s or­bit, de­spite con­tain­ing more ma­te­ri­al than sev­er­al Earths,”
Ra­goz­zine said, adding that they range from 1.3 to 2.6 times the size of the Earth by weight.

“At this rate, you could easily pack in 10 more plan­ets, and they would still all fit com­fortably in­side the Earth’s or­bit,” he said. The sys­tem lies in the di­rec­tion of the con­stella­t­ion Ly­ra, the harp, and is an es­ti­mat­ed 1,100 light-years away. A light-year is the dis­tance light trav­els in a year.

Ra­goz­zine and col­leagues used da­ta from NASA’s Kep­ler space mis­sion, which searches for plan­ets around dis­tant stars by ob­serv­ing over 160,000 stars at once and de­tect­ing small dips in a star’s bright­ness as a plan­et pas­ses in front. Kep­ler has in fact opened a new chap­ter in such re­search by disco­vering hun­dreds of plan­e­tary sys­tems with closely-spaced plan­ets, as­tro­no­mers say; KOI-500 is the most ex­treme of these.

“From the ar­chi­tec­ture of this plan­e­tary sys­tem, we in­fer that these plan­ets did not form at their cur­rent loca­t­ions. The plan­ets were orig­i­nally more spread out and have ‘mi­grat­ed’ in­to the ultra-com­pact con­figura­t­ion we see to­day,” said
Ra­goz­zine. Al­though re­cent the­o­ries for the forma­t­ion of the large plan­ets of the out­er so­lar sys­tem al­so in­volve plan­ets mov­ing dur­ing the forma­t­ion pro­cess, it is still un­clear how the in­ner plan­ets in the so­lar sys­tem, in­clud­ing Earth, avoided this fate.

Us­ing Kep­ler da­ta, as­tro­no­mers can meas­ure the sizes and or­bits of plan­ets or­biting Sun-like stars more pre­cisely than ev­er be­fore, giv­ing birth to a new sub­field of stu­dy. KOI-500’s plan­ets are so close to­geth­er, sci­en­tists say, that their mu­tu­al gra­vity pushes and pulls on their or­bits, caus­ing slight changes in the times that the plan­ets pass in front of their host star.
Using this ef­fect, Ji-Wei Xie, a post­doc­tor­al re­search­er at Nan­jing Uni­vers­ity
in China and the Uni­vers­ity of To­ron­to, re­cently con­firmed the two
can­di­dates or­biting far­thest from KOI-500 were really plan­ets.

Ragozzine’s work, still un­pub­lished, goes far­ther, con­firm­ing ad­di­tion­al plan­ets and
describ­ing their mass­es (weights) and or­bits. Ad­di­tion­al­, four of the plan­ets or­biting KOI-500 fol­low syn­chro­nized or­bits around their host star in a com­pletely un­ique way, he said: no oth­er known sys­tem con­tains a si­m­i­lar con­figura­t­ion. Work by
Ra­goz­zine and his col­leagues sug­gests migra­t­ion helped to syn­chro­nize the plan­ets.

“By pre­cisely char­ac­ter­iz­ing the del­i­cate ar­range­ment of plan­ets...
Kep­ler is pro­vid­ing in­sights in­to the forma­t­ion of KOI-500 and oth­er com­pact plan­e­tary sys­tems,” said Er­ic Ford, an as­tron­o­mer at the Uni­vers­ity of Flor­i­da and a con­trib­u­tor to the stu­dy.

“KOI-500 will be­come a touch­stone for fu­ture the­o­ries that will at­tempt to de­scribe how com­pact plan­e­tary sys­tems for­m,” added
Ra­goz­zine. “Learn­ing about these sys­tems will in­spire a new genera­t­ion of the­o­ries to ex­plain why our so­lar sys­tem turned out so dif­fer­ently.”

An extraordinarily crowded planetary system is providing clues for understanding why most known planetary systems seem different from ours, astronomers report.
Scientists are investigating KOI-500, a planetary system they say crams five planets into a region less than one twelfth the size of the Earth’s orbit.
Darin Ragozzine, a postdoctoral researcher at the University of Florida, presented findings about the system Oct. 15 at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences in Reno, Nev.
The five planets orbit their host star so closely that their years, the time they take to circle it, are measured at only 1.0, 3.1, 4.6, 7.1, and 9.5 days. All five “zip around their star within a region 150 times smaller in area than the Earth’s orbit, despite containing more material than several Earths,” Ragozzine said, adding that they range from 1.3 to 2.6 times the size of the Earth by weight.
“At this rate, you could easily pack in 10 more planets, and they would still all fit comfortably inside the Earth’s orbit,” he said. The system lies in the direction of the constellation Lyra, the harp, and is an estimated 1,100 light-years away. A light-year is the distance light travels in a year.
Ragozzine and colleagues used data from NASA’s Kepler space mission, which searches for planets around distant stars by observing over 160,000 stars at once and detecting small dips in a star’s brightness as a planet passes in front. Kepler has in fact opened a new chapter in such research by discovering hundreds of planetary systems with closely-spaced planets, astronomers say; KOI-500 is the most extreme of these.
“From the architecture of this planetary system, we infer that these planets did not form at their current locations. The planets were originally more spread out and have ‘migrated’ into the ultra-compact configuration we see today,” said Ragozzine. Although recent theories for the formation of the large planets of the outer solar system also involve planets moving during the formation process, it is still unclear how the inner planets in the solar system, including Earth, avoided this fate.
Using Kepler data, astronomers can measure the sizes and orbits of planets orbiting Sun-like stars more precisely than ever before, giving birth to a new subfield of study. KOI-500’s planets are so close together, scientists say, that their mutual gravity pushes and pulls on their orbits, causing slight changes in the times that the planets pass in front of their host star. By detecting this effect, Ji-Wei Xie, a postdoctoral researcher at Nanjing University and the University of Toronto, recently confirmed that the two candidates orbiting farthest from KOI-500 were actually planets.
Ragozzine’s work, still unpublished, goes farther, confirming additional planets and characterizing their masses and orbits. Additionally, four of the planets orbiting KOI-500 follow synchronized orbits around their host star in a completely unique way, he said: no other known system contains a similar configuration. Work by Ragozzine and his colleagues suggests migration helped to synchronize the planets.
“By precisely characterizing the delicate arrangement of planets in this extraordinarily crowded system, Kepler is providing insights into the formation of KOI-500 and other compact planetary systems,” said Eric Ford, an associate professor of astronomy at the University of Florida and a contributor to the study.
“KOI-500 will become a touchstone for future theories that will attempt to describe how compact planetary systems form,” added Ragozzine. “Learning about these systems will inspire a new generation of theories to explain why our solar system turned out so differently.”